<?php
/*
 *    Copyright 2012-2016 Youzan, Inc.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *        http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
namespace Zan\Framework\Utilities\DesignPattern;

trait Singleton {

    /**
     * @var static
     */
    private static $_instance = null;

    /**
     * @return static
     */
    final public static function instance()
    {
        return static::singleton();
    }
    
    final public static function singleton()
    {
        if (null === static::$_instance) {
            static::$_instance = new static();
        }
        return static::$_instance;
    }

    /**
     * @return static
     */
    final public static function getInstance()
    {
        return static::singleton();
    }

    final public static function swap($instance)
    {
        static::$_instance = $instance;
    }

}